The European parliament on Tuesday rejected a key report that would have toughened the EU stance on greenhouse gas emissions, after political wrangling that wrecked hopes of a compromise.

A rebellion by the UK's Tory MEPs helped to swing the vote against a tougher target on how much carbon emissions should be cut by 2020, but was not decisive, according to insiders.

The vote does not put an end to green campaigners' hopes of a more ambitious emissions reduction target – a higher cut of 30% by 2020 on 1990 levels rather than 20% – as the issue will continue to be debated, but is a setback.

The political wrangling involved a series of amendments, proposed by Conservative groupings of MEPs, that would have weakened the resulting resolution to an extent that was not acceptable to the Green MEP grouping.

Greens in the parliament will now try to push for the tougher target in future votes, and through the involvement of member states and the European commission.

Nick Stern, the former Treasury economist and now chair of the Grantham Research Institute on Climate Change and the Environment, said of the vote result: "It's a missed opportunity and the EU risks falling behind in the economic growth story of the future."

When the vote was originally scheduled to take place, on 23 June, a survey of Tory MEPs by the Guardian found that the leader of the Conservative party in the European parliament, Martin Callanan, was advising his colleagues to vote against the higher target, and several were planning to comply. Only one of those contacted in advance of the vote said she would definitely vote for the higher target.

The revelation prompted a parliamentary question to the prime minister, who vowed that he would persuade the MEPs. But a follow-up survey by the Guardian and Friends of the Earth has found that the prime minister has failed to convince them to vote for lower carbon emissions.

At least eight MEPs out of the grouping of 23 said they would vote against the measure, while most of the remainder did not respond to emails and calls. Only two MEPs said they would definitely vote in favour, and a handful were undecided.

Several MEPs echoed Martin Callanan, who told the Guardian: "Conservative MEPs have always been sceptical of the EU unilaterally increasing its target to 30% without a worldwide agreement. I am in favour of increasing the EU target to 30%, or even higher, in the context of a global agreement where our competitor countries take similar action. Increasing our own targets while the rest of the world does nothing will have virtually no measurable effect on global emissions, because it will force large EU emitters to relocate to other countries outside the EU where they will continue to emit at a much lower cost."

"We are also concerned that the higher carbon emission costs resulting from an increased target will feed through into energy price increases for domestic consumers," he said.

Their decision was attacked by the party's Liberal Democrat coalition partners, and by green campaigners.

Andy Atkins, executive director of Friends of the Earth, said: "As well as snubbing David Cameron, Tory MEPs are defying the latest scientific advice and playing fast and loose with our future. Preventing the necessary action on climate change also goes against EU economic interests – scores of Europe's leading companies back a 30% cut in emissions because it will create new jobs and business opportunities.

"David Cameron came to power with an intelligent approach to tackling climate change, but he must act fast to prevent his promise to lead the greenest government ever from unravelling. The prime minister must redouble his efforts to show his entire party the enormous benefits of building a cleaner, safer future," he added.